According to “Thrones” writer and producer Bryan Cogman’s book, “Inside HBO’s Game of Thrones: Seasons 1 & 2,” the prank occurred while shooting the eighth episode of season one. In the real, aired version, Snow sets a wight on fire at Castle Black while protecting Lord Commander Mormont (James Cosmo). But Harington didn’t initially get that version of the scene.

The producers sent Harington a script with a fake version of the scene. In it, Jon Snow pulls burning drapes from a fire and throws them at the wight. The fire, though, engulfs the both of them. In the end, Mormont exclaims, “Gods, boy. I was wrong about you. You’re a ranger, through and through!”

The scene ends with: “Jon smiles, his teeth shining brightly in his destroyed face. Mormont, sickened, has to look away.”

Harington was prepared to shoot the fire scene, which Weiss told him was the result of HBO being “worried the Jon Snow storyline was too Harry Potter, and they wanted to do something to make it darker.”